Telephone system



July 5, 1938. w. PINELL TELEPHONE SYSTEM Filed Dec. 4, 1956 3 Sheets-Sheet l INVENTOR. WALTER PIA/ELL ATTORNEY.

July 5, 1938. w. PINELL TELEPHONE SYSTEM Filed Dec. 4, 1936 5 Sheets-Sheet 2 INVENTOR. WALTER P/NELL ATTORNEY.

July 5, 1938. w. PINELL TELEPHONE SYSTEM Filed Dec. 4, 1956 3 Sheets-Sheet 3 1N VEN TOR. WALTEQ P/NELL ATTORNEY.

Patented July 5, 1938 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application December 4, 1936, Serial No. 114,102 In Germany December 10, 1935 Claims.

The present invention relates to telephone systems, and more particularly to systems in which facilities are provided whereby, while a main connection is being held, subsidiary connections can be set up over branch circuits associated with the main connection.

The invention may be applied with particular advantage in telephone systems in which subscribers engaged in a call have the facility for establishing enquiry calls or for signalling a supervisory station and in which the setting up of the enquiry call or the transmission of signals is dependent upon whether an enquiry connection has been established or not between two like switching measures which serve to initiate such connections. Previously in these systems a subscriber who after initiating an enquiry call by depressing a key, becomes convinced that the en quiry call is unnecessary or who has initiated an enquiry call by depressing the key unintentionally, could only restore the connection to its original condition through the collaboration of the supervisory station, since by depressing the key again, the supervisory station is signalled.

According to the invention these complications in operation are avoided in that a subsidiary connection, which is initiated by effecting a manual operation a predetermined number of times, is released and the main connection is restored to its original condition, if, prior to the completion of the subsidiary connection, the same manual operation is again effected a predetermined number of times. I

In one embodiment an enquiry call is initiated by performing a manual operation once and then dialling the required number, and a different subsidiary connection is initiated solely by performing the manual operation twice, a timing device becoming effective automatically, if impulses are not transmitted within a predetermined time after an enquiry call has been initiated, whereby any subsequent performance of the manual operation is prevented from completing the other subsidiary connection but is effective in restoring the main exchange connection to its original condition.

Since. a few seconds always elapse between the time of effecting the first depression of the key to initiate an enquiry call and the time when the subscriber realizes that the setting up of an enquiry connection is not necessary, then if the enquiry connection is to be released again by a second depression of the key, the timing device will always have taken effect when the second depression of the key is performed.

According to the invention the arrangement can alternatively be so arranged that the original condition of the connecting path is again set up by switching means under the influence of the enquiring subscriber only, in that the subscriber, if he wishes to neutralize the enquiry connection without dialing numerical impulses, effects the same manual operation (depression of a key) twice in quick succession. The first depression of the key initiates the transmission of a signal to the operator, whilst the second depression of the key controls devices which are set in readiness by the switching over operation for transmitting the signal, and bring about the re-establishment of the original condition of the connecting path. Thereupon the switching means serving to signal the operator are also released.

In addition to systems adapted for the selective initiation of enquiry connections or for the transmission of signals, the invention is also applicable in remote communication systems. The selective switching on of signals at various operating positions which can be connected to various points of a connecting path, or the selective operations of various signals at a single operating position may be referred to. operation of one signal is initiated by a single manual operation and the operation of another signal at a different point is effected by two manual operations, the invention makes it possible to suppress any inadvertent manual operation and to re-establish the original condition of operation of the connecting path without requiring the cooperation of an operator.

For simplifying the operation to be executed by the subscriber, the switching over devices and the auxiliary means for their control are so constructed that the subscriber need take no care as to the time during which he executes the switching operation in question so that he could thus effect switching measures, for example the depression of a key, whether for initiating the different switching operations or for suppressing them without having to take into account how long these switching measures must last in order toeffect the desired result.

The invention will be better understood from the following description taken in conjunction with the accompanying drawings, comprising Figs. 1, 2 and 3, which show three embodiments of the invention. All details, such as for example, controlling devices for seizing and setting connecting devices or for maintaining a connection, which are not necessary for the understanding of the invention, have been omitted for the sake of clarity since these are already known.

If for example, the

' the energizingwinding I of relay Yl.

Figure 1 shows a portion of a public exchange line extending to a private branch exchange sys tem, in which, dependent upon the varying number of times that the same switching operation is effected by a subscriber engaged in a call over this public exchange connecting line, either an enquiry call can be initiated or an operator can be signalled, and in which after an enquiry, call has been initiated and the enquiry connection has not been set up, the switching over operations, which prepare the restoration of the original condition of the line by a further similar switching operation on the part of the subscriber, are effected by a time switch.

Fig. 2 which is a modification of the invention,

shows'a portion of a public exchange line extending to a private branch exchange system, in which after initiation of an enquiry call by a depression of the key, the original condition of the connection may be re-established if the enquiry connection has not been set up by a double operation of the same key. The relays A2, X2, Z2, Y2, V2, E2, Dr3 and Ar2 correspond in operation to relays having the same reference letters but having the index I in Fig. 1.

Fig. 3, which is another modification of th invention, shows a portion of a public exchange line extending to a private branch exchange system, in which different signals are transmitted dependent upon the number of times the depression of the key is repeated by a subscriber.

Referring now to Fig. 1, when a call is initiated by a subscriber (not shown) in the private branch exchange, a battery feed. loop circuit is completed through the subscribers telephone for both windings of relays Al and Xl in series. In this circuit, only relay Al is energized and not relay Xl, since this is a differential relay, Relay Al establishes a direct current bridge between the leads I and 'l of the public exchange line over its contact tal in the following circuit; lead I, contacts 2arl, 32L 4al, relay Drl, contacts Sal, liarl, and lead I. The call in progress is maintained in the other exchange by the current flowing over this direct current path. In addition, by opening its contact Bel relay Al prevents the premature operation of relay El. Relay Drl energizes over the above direct current path and at contact ZSdrl the circuit for relay Vl is prepared.

If the subscriber wishes to set up an enquiry call, while maintaining the public exchange connection, he operates a key at his station and thereby connects earth (positive) to lead 9. Winding II of the differential relay XI is thereby short-circuited and at the same time the current through winding I of this relay is increased. Relay Xl energizes and closes its contacts lllzcl and llazl. For the present, however, only contact lfizrl is operative, because the contact Myl, arranged in series with contact I lml, is still open. Relay Zl is energized the following way over its winding I; positive, contact l2yl, winding I of relay Zl, contacts lllxl, l3yl and l lfl, and. negative. Relay Zl energizes and at contact l5zl prepares a locking circuit over its winding II and Both windings are short-circuited by contacts lfirl and l3yl. At contact llizl relay Zl connects the choke coil DrZ in shunt across leads l and T thereby ensuring the maintenance in the public exchange of the connecting path throughout the duration of the enquiry call. At contacts llzl and lliel the enquiry line Rl is'connected to the portion of the public exchange connecting path leading to the subscriber and simultaneously the portion of the public exchange connecting path leading to the public exchange is disconnected by the opening of contacts 32! and 52L When a subscriber releases the key, relay Xl falls back and contacts lllwl and llzrl are open. The following circuit is now completed: positive, contact lZyl, windings I and II of relay Zl, I of relay Yl, contacts l5zl, My! and negative. Relay Yl energizes. It closes contact lSyl and then opens its contact l2yl whereby the following locking circuit is established for relays Zl and Yl positive, contact l8yl, winding II of relay Yl, II of relay Zl, winding I of relay Yl, contacts liizl, l lfl, and negative. Contact ml is inserted in conductor 2| to prevent any premature operation of the enquiry switching devices. On the release of the key by the subscriber and the subsequent energization of relay Yl as described above, however, contact l9yl is closed so that the following direct current bridge is established between leads 20 and 2|: lead 20, contacts l'lzl, eal, relay Drl, contacts l8zl, lfiyl and lead Zl. By the current traversing this direct current bridge, a numerical impulsereceiver serving to receive numerical impulses from the enquiring station for setting up the enquiry connection, is set in readiness. At contact 22yl a thermorelay is connected up from: positive, contact 2211!, thermo-relay Thl, contact 23el and negative. The thermo-relay heats up. Contact 24' prepares for the transmission of signals to an operator.

When the subscriber transmits numerical impulses, these cause relay Al to release and at contact lal the impulses are transmitted to the impulse receiver of the enquiry path. Moreover, the slow to release relay Vl is energized over contact 25al and thus by closing contact 2lul establishes a circuit for itself independent of contact 26drl, and at contact 28121 short-circuits relay Dr! so as to ensure satisfactory impulse transmission. Relay Drl releases during the impulse train on account of the short-circuit. Relay Vl on the other hand remains energized, on account of its delayed release, during the opening bf contact 25al occurring during the impulse train.

The first numerical impulse for establishing the enquiry connection-also causes relay El, whose operation was prepared on the switching through of the enquiry line, to energize over the following circuit: positive, contact 8al, relay El, contact 29yl and negative. It looks up at contact 30el in a locking circuit independent of contact 8al, shunt contact i3yl by contact 3lcl and thereby prepares for the controlling of the switching over relay group Al and Yl by a further switching measure on the part of the subscriber. The open ing of contact 23el disconnects the thermo-relay Thl before the latter has had time to operate and by the opening of contact 32el prevents the operation of the relay Fl which causes the transmission of signals, due to any subsequent switching operation on the part of the subscriber.

When on the termination of the enquiry call, the enquiring subscriber wishes to re-establish the original condition of the connecting path, he operates his key a second time, i. e., the same switching operation which was effective for initiating the enquiry call. On account of the connection to earth by the keys at the subscriber's station relay Xl energizes again and closes contact lllxl. Since the contact 3lel, in series with contact lllxl, is closed, winding 11 of relay Zl and winding I of relay Yl are short-circuited.

Relay Zl releases and closes contacts 3zl and 5zl ating an enquiry call.

and opens contacts l'5zli, lBzl, l'lzl, and I8zl. In

place of the choke-coil DrZ, relay Drl is again connected across the leads I to 1 so long as the subscriber holds the'key down. Relay Yl remains energized over: positive, contact l8'yl, winding II of relay YI, contacts Iflxl, 3lel, Mfl and negative. When the subscriber releases the key, relay XI falls back again and opens its contact lllxl, thereby breaking the locking circuit for relay Yl which releases and restores all its contacts to normal.

The condition of the connecting path which was obtained before the first depression of the key by the subscriber (for initiating an enquiry call) is once more established.

7 If the subscriber wishes to signal an operator he has to depress the key at his station twice. By the first operation of the key the switching over relay group comprising relays Zl and Yl is operated in the same way as in the case of initi- The second depression of the key influences relay Fl, since the differential relay XI operating for the second time closes the following circuit: positive, contacts 24yl', llatl, relay Fl, contacts 32el, 33arl and negative. Relay Fl energizes, establishes a locking circuit independent of contacts llacl and 24yl by closing its contact 35fl and opens contact I MI and thereby breaks the locking circuit over the windings of relay Yl and Zl so that both these relays release and restore their contacts to normal with the result that the enquiry switching is released and the thermo-relay Thl is disconnected before it energizes. At contact 36H the supervisory lamp: ULl is switched on over: positive, contacts Slarl, 36fl, ULl and negative.

If the operator after noting the lighting of the lamp ULI wishes to connect to the public exchange line she operates the switch ATl thereby energizing relay ARI which by opening contact 33ml breaks the locking circuit for relay Fl, disconnects the lamp ULl at contact 3'larl, at contact 38arl connects the choke coil Dr2 across the leads I and l of the public exchange line and by closing contacts 390ml and Mlarl couples the branch line leading to the operators speaking apparatus with the portion of the public exchange connecting path leading to the signalling subscriber, while simultaneously disconnecting the leads I and l. v

If after the subscriber has conversed with the operator it is desired to re-establish the originalcondition of the connecting path, the operator restores the switch A'Il to normal and relay ARI releases the switches through the speaking leads.

The case will now be considered in which the subscriber, after initiating an enquiry call, i. e., after the enquiry line RL has been connected up through the influencing of the switching over rerelay group Zl and Y], comes to the conclusion that the establishment of the enquiry call is unnecessary. The thermo-relay Thl connected up at contact 22yl becomes operative after a few seconds and closes its contact llthl and thereby energizes relay El whose energizing circuit has been prepared'at contact 2911! when the first depression of the key which initiated the enquiry call, becomes operative. Relay E. establishes a locking circuit independent. of contact Mthl at contact 30el, at contact 23e'l breaks the circuit for the thermo relay and by closing contact 3 lel prepares for thecontrolling of the switching over relay group Zl and Yl by a further similar switching operation (depression of the key) on the part of the subscriber. When the subscriber executes this switching operation relay XI energizes again and at contacts llkcl short-circuits winding I of relay Yl and winding II of relay Zl. Relay Zl releases. After the key is released relay Yl falls back as already described'above.

The condition of the enquiry path obtained before the first depression of the key, which promoted the enquiry call is once more re-established. It should be mentioned that the second depression of the key does not result in connecting up the supervisory lamp ULl in spite of the closing of contact llatl since relay El energized by the thermo-relay Thl breaks the energizing circuit of relay Fl at contact 326i.

Figure 2 shows the embodiment in which after initiating an enquiry call by a depression of the key the original'con'dition of the main connecting path may be re-established if the enquiry connecting path is not set up by a double operation of the same switching means (depression of the key). The relays A2, X2, Z2, Y2, E2, Dr3 and A12 correspond in operation to the relays having the same reference letter but having the index I in Fig. 1.

During a call relay A2 is energized and its contact 5M2 is closed whereby relay Dr3 is connected across the leads 5| and 52 of the public exchange line, premature operation of relay E2 is prevented at contact 53112, and contact 54a2 fulfills the same function for relay V2. If the subscriber wishes to set up an enquiry call he earths his speaking line. Relay'XZ energizes and closes contact 55202. Relay Z2is energized, closes its contacts 5522, 5622, 51z2 and 5822 and opens its contacts 5922 and 6522. On releasing the key, on account of the removal of the short-circuit about Winding II of relay Z2 and winding I of re lay Y2, relay Y2 energizes and opens its contact 6ly2 and at contact 623/2 switches the enquiry line through. At contact 63112 it prepares for the energizing of relay E2 and .at contact 64112 it prepares for the controlling of the second switching over relay'group comprising relays F2 and G2.

When the subscriber transmits numerical impu ses for establishing the enquiry path, the relays EZ and V2 energize in the same Way as do the relays El and VI in the embodiment of Fig. 1. Relay E2 locks up at contact 6522 in circuit independent of contact 53112 and at contact 6682 prepares for the controlling of the switching over relay group Z2 and Y2 by a further depression of the key on the part of the subscriber and by opening contact 5162 prevents the second switching over relay group comprising relays F2 and G2 from being controlled by the same depression of thekey by the subscriber. Relay V2 is energized during each impulse train since it establishes a locking circuit independent of contact 59dr3 at contact 68222 and short-circuits relay Dr3 in the bridge across the enquiry line RL at contact 1002.

If after terminating the enquiry call the subscriber desires to re-establish the original condition of the connecting path he operated his key once more. Relay X2 energizes and the winding II of relay Z2 and the winding I of relay Yl are short-circuited. Relay Zl falls back, switches the speaking leads through to the public exchange line conductors 5! and 52 and disconnects the choke coil D14. On releasing the key the circuit for winding 11 of relay Y2, completed over contact 101/2 is broken through the release of relay X2 and the opening of contact 55x2.

Relay Y falls back and restores all its contact to the normal position shown in the drawings.

The condition obtained in' the connecting path before the initiation of the enquiry call is now re-established.

If the subscriber wishes to signal the operator by connecting up the lamp UL2 he has to depress his key twice. The first depression of the key results in the energizing of relays Z2 and Y2. At contact 6411/2 preparation is made for controlling the relay group F2 and G2 and simultaneously, by opening contact 6Iy2, the switching over relay group Z2 and Y2 is prevented from being influenced by the next depression of the key. When relay X2 energizes in response to the second depression of the key the following circuit is established at contact lla22: positive, contacts 641/2, 12 2, winding I of relay G2, contacts 1!.1'2, G162, WW2 and negative. Relay G2 energizes and at contact l4g2 prepares a circuit over its winding II and the winding I of relay F2. On releasing the key, relay X2 falls back and opens contact 1 I372. Relay F2 con now energize over the following circuit: positive, contacts 64y2, 12f2, windings I and II of relay G2, Winding I of relay F2, contacts g2, 6le2, 130.12 and negative. Relay F2 energizes and locks up by closing its contacts 18 2 .and 1612 in a circuit independent of contact 64312: positive, contacts 1812, IE/2, winding II of relay F2, winding II of relay G2, winding I of relay F2, contacts I492, 6ie2, 13ar2 and negative. By the opening of contact "f2 the locking circuit for relays Z2 and Y2 is broken. Both relays accordingly release and restore their contacts to normal. Thus, the enquiry connection is thereby released. At contact 19]2 a delay device for example a. thermo-relay Th2 is connected up which becomes operative after short time and connects up relay F3 at contact th2; positive, contacts 19 2, 80th2, relay F2 and negative. Relay F3 energizes, establishes a locking circuit independent of contact 801712 at contact 8H3, breaks the heating circuit for the relay Th2 at contact 82 3 and at contact 83f3 completes the circuit for the lamp UL2 from: positive, contacts, 84ar2, 83 3, lamp UL2 and negative. The operator connects up to the line leading to the sub scriber transmitting the signal while time disconnecting the leads 5| and 52 leading to thepublic exchange by operating the switch ATZ and thereby energizing relay A2 which closes contacts 85ar2, 860012. and 8lar2, and opens contacts 83ar2 and 891112 the locking circuit for relays F2 and G2 is simultaneously open at contact l3ar2. The subscriber and the operator can now converse together. connects by restoring the switch AT2, relay Ar2 de-energizes and restores all the contacts to normal. The condition of the connecting path obtained before the first depression of the key is once more re-established.

The case will now be considered where the subscriben after executing the first switching operation (depression of the key) and thereby controlling the switching over relay group Z2 and Y2 to connect up the enquiry line RL, makes up his mind that the establishment of the enquiry call is unnecessary. In order to re-establish the originai condition of the connecting path he operates the key at'his station twice. By the first depression of the key, after that initiating the enquiry call, the switching over relay group comprising relays G2 and F2 are controlled in the manner described, the thermorelay Th2 heats up and delays the lighting of the supervisory lamp UL2. When now shortly afterwards the subscriber depresses the key again F2 are short-circuited. Relay G2 releases.

at the same When the operator disthis has the consequence of energizing relay X2 which short=circuits winding II of relay G2 and winding I of relay F2. .Relay G2 releases and opens its contact 1492 Only relay F2 now remains connected up over its winding II from: positive, contacts 18 2, 16 2, winding II of relay F2, contacts H322, 6le2, 131112 and negative. 0n releasing the key, relay, X2 falls back and opens the contact Hrc2. Relay F2 releases and disconnects the thermo-relay.

The condition obtained before the inadvertent initiation oi the enquiry call is once more reestablished.

If the operator does not reply after the iamp UL2 has been lighted or if the subscriber decides to abandon the connection to the operator before the latter has responded he has it in his power to re-establish the original condition of the connecting path. The switching over relay group G2 and F2 also serves this purpose. The subscriber has merely to depress his key once more. Relay X2 energizes. At contact 11x2 winding II of relay G2 and winding I of relay Contact M92 opens. On releasing the key, relay X2 falls back and contact Hx2 opens. Relay F2 die-energizes and at contact l9f2 breaks the circuit for relay F3 or, if this has not yet been connected up, that of the thermo-relay Th2. Since contact "f2 is also closed, the original condition of the connecting path is re-established.

Figure 3 represents the invention applied to a system in which different signals are transmitted dependent upon the number of times a switching operation (depression of a key) is repeated on the part of a subscriber. It is assumed that a lamp UL3, of the exchange VStI to which the subscriber is connected, is lighted by a single depression of the key, whilst when the switching operation is operated twice, a lamp UL2 is lighted the exchange 'VSt2. As before, battery feed is supplied to the calling subscriber by relays A3 and X3. Relay A3 over its contact lElllaB maintainsenergizedrelay A4 located in the bridge 4 arrangedat the exchange V8152 from: negative, winding I of reiays X4 and A4, lead NH, contacts I2 'i04, |0la.3, choke-coil Dr5, lead 134, windings II of relays A4 and X4, and'positive. Relay X4 is a differential relay and cannot energize in this circuit.

To light the lamp UL3, the subscriber operates his key and thereby applies earth to his speaking line conductors. Relay X3 operates and at contact l05at3oompletes a circuit: positive, contact l06y3, winding I of relay Z3, contacts 35x3, Ink 3, relay V3, contacts lll8ar3, I3Eth3 and neg ative. Relays Z3 and Y3 energize. Relay V3 serves a purpose to be explained later. Relay Z3 at contact H1923 prepares an energizing circuit over winding I of relay Y3 and a locking circuit over its own winding II. The relay V3 shunting this winding has so low a resistance that relay Y3 cannot energize so long as contact M5303 is closed. When the key is released, relay X3 de-ener-gizes and contact M5003 opens. Relay Y3 can now energize over its winding 1. It connects up its own winding II in place of'winding I of relay Z3 over contact M3113 and at contact l i ly3 prepares for connecting up'the lamp The contacts I'i2y3 and H3y3 which are likewise closed serve purposes tobe explained later. The opening of contact lul 3 prevents any premature influencing of the switching over relay-group Z3 and Y3. When, on account of the opening of contact 105:03, the slow to release relay V3 de-energizes, the circuit for the lamp UL3 is closed: positive, contacts H4123, llly3, H504, H5125, Hlar3, lamp UL3 and negative. The operator is informed by the lighting of the lamp UL3 that the subscriber wishes to converse with her. She operates the switch AT3 and thereby energizes relay Ar3 which connects a branch line leading to her speaking equipment to' the connecting path by closing contacts 8:113 and Il9ar3. Relay A13 by opening contacts l2ilar3 and I2'lar3 disconnects the connecting line leading to public exchanges, at contact H'iar3 breaks the circuit for the lamp UL3, and at contact [081113 breaks the locking circuit for relays Z3 and Y3.

On the termination of the conversation between the subscriber and the operator the switch AT3 is restored, relay A13 releases and restores its contacts to normal and the original condition is re-established.

The case will now be considered in which the subscriber wishes to signal the operators station at the exchange VStZ. For this purpose he has to depress the key at his station twice in quick succession. The first depression of the key once more controls the switching over relay group Z3 and Y3. Relay V3, which was energized, delays the lighting of lamp UL3 so that when the subscriber depresses the key a second time directly after the first, in order to operate the lamp at the operators position at the exchange VS-t2, the lighting of lamp UL3 is prevented in that the relay X3 energizing again in response to the second depression of the key and closes, at con tact I22m3, the circuit which was prepared for relay V4 at contact I i2y3. This relay-opens contact H5124 thereby breaking the circuit for lamp UL3 and in addition prepares a circuit for relay V at contact H304.

Relay V4, which is energized during the time that the key is depressed at the station and while relay X3 is energized also initiates the switching on of the signal at the operators position in the exchange VStZ. For this purpose it closes contact 2404 and thereupon opens contact, [02124. Winding II of relay X4 in the exchange VStZ is disconnected and relay X4 is energized over its winding 1, whilst relay A4 remains energized over its winding I arranged in series with winding I of relay X4. Relay X4 closes contact l25a34 and thereby completes the following circuit: positive, contact |26y4, winding I of relay Z4, contact l25m4, relay V6, contact 1311., and negative. Relay Z4, at contact 121.24, prepares a circuit over its winding II and over winding I of relay Y4,

whilst relay V6 opens its contact 128125 and therer by delays somewhat the switching on of lamp UL4 after the key is released. When the key is released by the subscriber, relay X3 falls back as does relay V4 which closes contact M204 and opens contact [2404. Relay X4 ole-energizes and. opens contact l25x i. Relay Y4 can now energize over its winding 1, since the winding of relay V5 arranged in series over contact I25ac4 is of so low a resistance that Y4 did not receive suiiicient current to energize so long as contact l25a34 was closed. Contact |29y4 is closed. Winding II of relay Y4 is now connected up in place of winding I of relay Z4. Contact I301 is moreover closed and accordingly the lamp UL4 is lightedafter relay V6 has released over the following circuit; positive, contacts l30y4, 128125, l3lt, lamp-UL4 and negative.

In thee'xchange VStl, the releaselof relay X3 completes the circuit for relay V5 which was prepared at contact I23o4 when relay V4 energized: positive, contacts l3l.'r3, [2304, HMS, relay V5 and negative. Relay V5 closes its contact 133115 and then opens its contact 132125. It has now established a locking circuit which is dependent only upon contact I l3y3. The closing of contact l34v5 prepares a circuit for controlling of the switching over relay group Z3 and Y3 by the subscriber, whilst a thermo-relay Th3 is connected up at contact I352 5. The thermo-relay Th3 operates after a certain time and opens contact I35th3 and thereby causes the disconnection of relay Z3 and Y3. Relay V5 now also falls back since contact H3113 is open.

When the operator at the exchange VStZ enters the connection in response to. the lighting of lamp UL4, the contacts I3lt and 131i are opened in any desired manner and the lamp UL4 is disconnected while the locking circuit for relays Z4 and Y4 is broken. When at the termination of the conversation between the subscriber and operator at the exchange VStZ the latter disconnects and contacts Hit and l3lt are again closed the condition obtained before the subscriber effected the first switching operation is again established.

The case will now be considered in which the subscriber has inadvertently operated the key once. This results in the energizing of relays Z3 and Y3 and also of relay V3 which delays the connecting up of the supervisory lamp UL3. If the subscriber now operated the key twice in quick succession, no lighting of the lamp UL4 occurs, but the original condition of the connecting path is re-established. If the key is depressed a second time by the subscriber after relay V3 has already released, the transitory switching on of the lamp UL3 has no significance since some timemust always elapse before the operator enters the connection after the lamp has lit up. The slow operating relay V3 can however be made sufiiciently slow to operate so that in the majority of cases operation of the lamp UL3 is definitely prevented.

The second depression of the key on the part of the subscriber causes relays V4, X4 and Z4 to energize again and after the key has been released relays V5 and Y4 energize. If now the subscriber depresses the key once more winding II of relay Z3 and winding I of relay Y3 are short-circuited in the exchange VStl by contacts 35.103 and H405 which are arranged in series. Relay Z3 releases. At contact l22x3, relay V4 is switched on and energizes relay X4 over contact 12404. This latter relay closes contact I25m4 thereby connecting the low resistance winding of relay V6 in parallel with winding II of relay Z4 and winding I of relay Y4. Relay Z4 releases. Relay V6 energizes and prevents the lamp UL4 being switched on at contact I28v6.

When the subscriber releases the key, contacts x3 and l22rr3 open and relay Y3 falls back. In addition relay V4 de-energizes. Relay X4 falls back, contact 125204 opens and relays Y4 and V6 release. The release of relay Y3 causes relay V5 in the exchange VStl to release upon the opening of contact H3113. The connecting path reverts to the original condition obtained before the first inadvertent switching operation on the part of the subscriber.

In the drawings it is shown that, when a connecting path is restored to its original condition after switching operations initiated by the operation of the key on the part of a subscriber 75 have become efiective, all the control and switching over devices also revert to their original condition. This is, however, not always necessary. In the case of special forms of system or if special control devices, for example electro-magnetic switches, are used as controlling devices, the control and switching over devices can of course be brought to a condition other than that in which they were to be found before the subscriber initiated the switching operations. sumption made is that the connecting path as regards its operating condition always assumes the same condition, after all the switching operations have been effected by the subscriber, as that obtained before the switching operation took place.

What is claimed is:

1. In a telephone system, a switching device, a trunk line extending to a public exchange, a branch line associated with said switching device, means operative responsive to the seizure of said switching device by a calling subscriber for seizing said trunk line, means controlled by a manual operation a predetermined number of times by the calling subscriber for controlling said switching device to maintain said trunk line in its seized condition, for disconnecting said trunk line from said switching device, and for seizing said branch line to connect the calling subscriber thereto, and means for again connecting the calling subscriber to the seized trunk line responsive to the same manual operation by the calling subscriber a predetermined number of times prior to the completion of a connection over the seized branch line.

2. In a telephone system, a switching device, a trunk line extending to a main exchange associated with said device, a branch line over which inquiry calls are extended associated with said device, an incoming line over which a subscriber may seize said device, means in said switching device operative responsive to the seizure of said switching device by a calling subscriber for seizing said trunk line, means in said switching device controlled by a predetermined number of manual operations performed by the calling subscriber for maintaining said trunk line in a seized condition, for disconnecting'said trunk line from said switching device, and for seizing said branch line and connecting the calling subscriber thereto, means in said switching device for repeating impulses transmitted by the calling subscriber over said branch line to complete a connection thereover, a timing device associated with said switching device, means for starting said timing device when said branch line is seized, means controlled by said timing device after a predetermined time interval has elapsed for disconnecting said branch line from said switching device and for again connecting the seized trunk line to said switching device and calling subscriber, and means in said switching device operated responsive to the transmission of the impulses for extending said connection over said branch line for preventing said timing device from performing said controlling operations.

3. In a telephone system, a switching device, a trunk line extending to a main exchange associated with said device, a branch line over which inquiry calls are extended associated with said device, an operators line associated with said device and normally disconnected therefrom, an incoming line over which a calling subscriber controls said device, means in said device operative responsive to the seizure thereof by a calling subscriber for seizing said trunk line, means The only as-' in said device controlled by a predetermined number of manual operations by the calling subscriber for maintaining said trunk line in its seized condition, for disconnecting said trunk line from said device, and for seizing said branch line and connecting the incoming line thereto, a signal for the operator associated with said operators line, means in said device controlled by said predetermined number of manual operations plus one additional manual operation by the calling subscriber for operating said signal, means controlled by the operator for maintaining said trunk line in its seized condition, for disconnecting said trunk line from said device, and for connecting said operators line with said device and said incoming line, a timing device in said switching device, said timing device effective when impulses are not transmitted by the calling subscriber to control the extension of a connection via said enquiry line within a predetermined time interval for preventing any subsequent manual operation by the calling subscriber from controlling said operators signal and for controlling said switching device to disconnect said branch line from said switching device and for reconnecting said trunk line to said switching device and incoming line.

4. In a telephone system, a switching device, a trunk line connected thereto, a first branch line, a second branch line, said branch lines associated with said device and normally disconnected therefrom, an incoming line over which a calling subscriber may seize and control said device, means in said device operative responsive to the seizure thereof by a calling subscriber for seizing said trunk line in order to complete a connection between the incoming line and the trunk line, switching means in said device controllable over said incoming line for disconnecting said incoming line from said trunk line, for seizing the first of said branch lines and connecting the incoming line thereto responsive to a predetermined number of manual operations by the calling subscriber, said switching means also controllable responsive to a predetermined different number of manual operations by the calling subscriber to disconnect said incoming line from said trunk line, to seize the second of said branch lines and to connect the incoming line thereto, means controlled by said switching means for holding said trunk line in its seized condition when either one of said branch lines is seized, said switching means effective to restore the initial connection between the trunk line and the incoming line prior to the completion of a connection over either one of said branch lines responsive to the .same number of manual operations by the calling subscriber required to initiate the seizure of the first of said branch lines.

5. In a telephone system, a switching device, a trunk line connected thereto, a first branch line, a second branch line, said branch lines associated with said device and normally disconnected therefrom, an incoming line over which a calling subscriber seizes and controls said device, means in said device operative responsive to the seizure thereof by a calling subscriber for seizing said trunk line in order to complete a connection between the incoming line and the branch line, switching means in said device controllable over said incoming line by a single manual operation by the calling subscriber for disconnecting said incoming line from said trunk line, for seizing the first of said branch lines and for connecting the incoming line thereto, said switching device also responsive to the same manual operations being performed twice for disconnecting said incoming line from said trunk line, for seizing the second of said branch lines and for connecting the incoming line thereto, means controlled by saidswitching means for holding said trunk line in seized condition when either one of said branch lines is seized, said switching means also operable responsive to two further similar manual operations in quick succession by the calling subscriber to restore the initial connection between the trunk line and the incoming line after an inadvertent single manual operation has initiated the seizure of the first of said branch lines.

6. In a telephone system as claimed in claim 2, in which the timing device is a thermal relay that energizes after a predetermined elapsed time interval only when impulses are not transmitted by a calling subscriber within that elapsed time intervals.

7. In a telephone system as claimed in claim 2, in which the means controlled by the timing device is a relay that energizes and thereby initiates the disconnecting of the branch line and the reconnecting of the seized trunk line.

8. In a telephone system as claimed in claim 1, in which the means controlled by the manual operation is a relay group.

9. In a telephone system, a repeater, a trunk line over which connections are extended to a main exchange associated with said repeater, an incoming line over which a calling subscriber seizes said repeater, means in said repeater operated responsive tothe seizure thereof Ior seizing said trunk line, a branch line over which enquiry connections may be extended by the calling subscriber while he holds the seized trunk line, means in said repeater controlled over said incoming line responsive to a single operation of a key by the calling subscriber for connecting said incoming line to said branch line and disconnecting said trunk line therefrom and for holding said trunk line in a seized condition, while the subscriber extends a connection over said branch line, a second branch line extending to an operators position, a signal at said position, means in said repeater controlled over said incoming line responsive to two operations of a key by the calling subscriber for operating said signal, and means in said repeater controlled by the operator at said position for connecting said incoming line to said second branch line and for disconnecting said trunk line therefrom and for holding said trunk line in a seized condition.

10. In a telephone system as claimed in claim 9, in which said repeater may be controlled while said incoming line is connected. to the first of said branch lines to disconnect the incoming line from the first of said branch lines and to reconnect it to the held trunk line responsive to a further operation of the key by the calling subscriber or may be controlled while said incoming line is connected to said second branch line to disconnect the incoming line from said second branch line and to reconnect it to the held trunk line responsive to the operation of a key by the operator at said position.

WALTER, PINEIL, 

